1. Field of the Invention
This invention relates to devices and systems for providing electrostatic charging of dry sorbent particles for injection into a polluted gas stream for the remediation of pollutants in that gas stream.
2. Purpose of the Invention
The invention provides a self or continuous purging electrostatic gun type device for use in a remediation and elimination of major industrial pollutants as are found in a flue gas stream. The invention provides for greatly improving sorbent particle charging efficiency over earlier like devices. The invention is for utilization in a system for the removal of a majority of the pollutants as are by-products from coal-fired power plants, soil remediation plants, steel plants, chemical plants, smelters and municiple incinerators. Pollution remediation systems as would employ the invention are commonly known as dry systems that have been shown to require a significantly lower capital investment than that required for wet systems, but, prior to the present invention, have not performed as efficiently as such wet systems.
3. Prior Art
The present invention is used in a practice of a dry flue gas remediation process that involves a utilization of electrostatically charged dry sorbent particles for introduction into a polluted gas stream in the remediation of pollutants in that gas stream. Such sorbent injection systems involve three major systems to maximize charged sorbent particle density and minimize reaction time and sorbent usage. The systems provide for the management of the sorbent particle flow rate, sorbent particle feed rate, and the generation of a corona discharge to provide sorbent particle charging and its control, for a specific sorbent compound. Sorbent compounding includes sorbent selection and a determination of both the sorbent flow and feed rate, and is based upon the type and amount of pollutant(s) as are present in a gas stream. Compounding also takes into account the chemical reaction rate of charged sorbent particles to pollution particles and is a surface phenomena. Accordingly, the type of sorbent material that is selected, its concentration and particle size will greatly effect charging effectiveness and therefore the costs of system operation. The characteristic of the selected sorbent include: its density; hygroscopic properties; and the like, are used to calculate the rate of feed.
Summarizing, the sorbent feed rate is determined by the stoichiometric properties of the pollutants and the selected sorbent, with the sorbent injection and the flow rate of air injected into the sorbent flow selected to minimize the volume of air that enters the flue gas stream.
The present invention, for use in such remediation system, provides a charging gun that is operated to generate a corona discharge around a charging electrode wherethrough the sorbent is directed and provides, during system operation, a purging air flow directed across a grounding ring or rings, that prohibits sorbent particles for collecting thereon.
The electrostatic gun of the invention provides for charging dry sorbent particles that are then injected into a polluted gas stream to create a large charged surface area in that gas flow or stream for enhancing the chemical reaction between the pollutants and sorbent. Such electrostatic guns and systems for their use are, of course, not new. However, while such have heretofore been available, they have not, prior to the present invention, achieved the sorbent charging efficiency of the present invention that is a dramatic improvement over such earlier devices. For example, a device of one of the present inventors, U.S. Pat. No. 5,312,598, shows an electrostatic charging gun for use in a system to provide for remediation of pollutants in a gas stream and for removing charged pollution particles therefrom that the present invention improves upon. Also, an improved electrostatic charging gun of two of the present inventors is shown in a U.S. patent application Ser. No. 08/429,082, entitled, "Electrostatic Gun for Injection of an Electrostatically Charged Sorbent into a Polluted Gas Stream". Further, other U.S. patents of one of the present inventors, U.S. Pat. Nos. 5,308,590 and 5,332,562, show a utilization of an electrostatic charging gun in a remediation system. Additionally, other examples of electrostatic charging guns and antenna particle charging devices are shown in U.S. patents to Schuff, U.S. Pat. No. 4,220,478; and U.S. Pat. No. 4,290,786. Neither of which Schuff patents shows an electrostatic charging arrangement that is like that of the present invention in either its structure or functioning.
The above cited U.S. Pat. No. 5,312,598, and patent application each show an electrostatic charging gun with a proven capability for charging sorbent particles in a sorbent material flow that is directed therethrough. While, in practice, each of these charging guns has proven to be effective, when used in an apparatus like that of the above cited U.S. Pat. No. 5,308,590, each charging gun has failed to consistently charge a high percentage of sorbent particles in the sorbent flow. To compensate, a higher volume of sorbent material has been required to be used than would be necessary if the percentage of charged particles in the flow were improved. For the gun of U.S. Pat. No. 5,308,598, the charging failure occurred because a corona discharge produced around a charging electrode of the gun did not extend across the gun barrel. Whereas, for the improved electrostatic gun of the above cited U.S. patent application, it has been found that sorbent particles tended to collect on the surface of charging rings, interfering with the formation of a corona discharge across the gun barrel between the charging electrode and grounding ring surfaces. The electrostatic charging gun of the invention provides for and maintains, a purging air flow directed over a grounding ring, insuring the maintenance of a corona discharge at the electrode and a dense field of free electrons that extend from the charging electrode to the grounding ring, wherethrough a continuous even flow of sorbent particles are directed. The grounding ring or rings are thereby kept free of sorbent particles as collected thereon that interfere with a corona discharge generated at the charging electrode that the discharge to thereby extend essentially across the sleeve end, greatly improving particle charging efficiency over earlier electrostatic charging guns. Sorbent particle charging is thereby more efficiently provided and at a decrease in required electrical power over earlier systems.